1. Field of the Invention
The invention relates to the use of a thermosetting synthetic resin in the production of products based on mineral fibers, in particular glass fibers such as mineral fiber mats which are employed in the manufacture of thermal insulation and/or in the soundproofing of buildings.
2. Description of the Background
Most mineral-fiber based insulating materials employ a binder for the fibers which ensures the mechanical strength of the material, i.e., it binds the fibers together. The binder must be dispersed homogeneously among the fibers in order to avoid forming bundles of fibers surrounded by lumps of binder within a group of more brittle and therefore dustier fibers. The binder is always used in a diluted state in a size.
It is known to use a thermosetting phenolic molding resin (phenol-formaldehyde) or an aminoaldehydic resins (melamine-formaldehyde or ureaformaldehyde) resin as a binder. The most frequently used binders are resols which are the products of the condensation in the presence of alkaline or alkaline-earth catalysts, of phenols, having open ortho- and para-sites, and aldehydes, primarily formaldehyde. These resins form a size which, in addition to water, contains urea which serves to reduce the free formaldehyde content and also acts as a binder, along with various additives such as oil, ammonia, coloring agents and, if necessary, fillers.
There are very many criteria, and of different types, involved in the selection of a binder, without forgetting however that a binder must above all adhere correctly to the glass.
First, it is essential that the binder be rheologically compatible with the fiber manufacturing process. Without going into unnecessary details, the glass fibers are usually produced using a centrifuge with a vertically oriented axis into which a continual jet of molten glass is introduced. The glass is sprayed towards the peripheral wall of the centrifuge from which it escapes in the form of filaments through a multitude of tiny orifices. The filaments produced are drawn out and pulled downwards by a high temperature high pressure gas current. The fibers obtained are collected on a gas permeable conveyor and thus form a mat of varying thickness depending on the speed of the conveyor.
The size should ideally coat each fiber produced in this way perfectly. It is therefore preferable to spray the size compound onto the fibers while the fibers are still separate, i.e., before the mat is formed. Consequently, the size is sprayed into the fiber reception hood, below the burners which generate the gas current to draw out the fibers. As a corollary to this operation it is forbidden to use inflammable organic solvents and/or pollutants in formulating the size, since the risk of fire and/or pollution in the reception hood is too high. In addition, the resin serving as binder must not polymerize too rapidly before taking on the desired shape.
Furthermore, although this polymerization should not be too rapid, it should not take too long. However, on this point, resins currently in use are not perfectly satisfactory since complete polymerization is achieved in a time compatible with a high production rate only after remaining in a high temperature oven at approximately 250.degree. C. which is a high power consumer.
Lastly, the resin and its implementation process must be of relatively moderate cost which is compatible with that of glass fiber manufacture and must not lead either directly or indirectly to the formation of toxic or polluting effluents. In this respect, a choice by an industrial concern has been to select resins which do not require the use of formaldehyde in their manufacture, and which in addition do not release significant quantities of formaldehyde when they decompose under the effects of great heat. In such conditions, the product is, of course, non-toxic and in addition does not give off an unpleasant odor if it should burn.
In an industry associated with the insulating glass fiber industry, i.e., the reinforcement glass fiber industry, it is known to sheath glass fibers with an epoxy resin. The sizing operation has the double object of protecting the fibers individually so that they are thus less sensitive to friction and offer better bonding to the plastic material for which the fibers act as reinforcement. But in this case, there is no attempt to link the glass fibers and nothing allowed concluding that glass/glass bonding was sufficiently solid for good mechanical resistance and localized throughout the total thickness.